1. Field of the Invention
This invention relates to vessel propulsion systems, and in particular to a self-contained hydraulic thruster for vessel.
2. Background of the Invention
Marine thrusters typically mount on barges and flat boats, and are used as propulsion for these vessels. One type of marine thruster employs a prime mover such as a diesel engine driving a hydraulic pump, together known as a “power pack”, and the resultant pressurized hydraulic fluid may be employed to drive a propeller attached to a lower unit.
One major problem associated with marine thrusters has been that where a centrally located tiltable lower unit has been retracted and tilted backwards for storage, maintenance, cleaning, etc., the protruding upper end of the lower unit interferes with the helm and helm platform, and prevents full upward tilting of the retracted lower unit. This problem was solved by U.S. Pat. No. 7,654,875 granted to Williams, incorporated hereinto by reference, which provided lower units laterally offset from a base and helm platform, thus avoiding interference between the lower unit(s) and helm platform when tilting retracted lower unit(s) forward for storage or shipping.
However, there are still a number of problems associated with currently available marine thrusters. One problem is the absence of a strong, redundant tilt actuator system whose components are not immersed in water, thus reducing corrosion due to moisture.
Another challenge involves providing positive down-tilt stops which provide mechanical end-of-downwards-tilt travel stops, so that the lower unit is held securely vertical when tilted down, especially when developing thrust.
Still another problem is being able to provide means to position the marine thruster on a vessel deck without permanent downwards-protruding member(s), because such downwards-protruding member(s) interfere with storage and shipping by increasing the overall height of the unit.
Another problem with current designs is the lack of an effective extension and retraction mechanism for lower units which provides long extension/retraction travel. Long travel extension is especially important where the hydraulic thruster is to be installed on deep draft vessels.